On the early behavior and microstructure of oil well cement paste incorporating with carbon nanotubes cured at a high temperature

Abstract

With the rapid development of shale gas/oil exploitation, hostile downhole condition asks for more flexible and ductile oil well cement paste (OWCP). This study is devoted to investigating the influence of multi-walled carbon nanotubes (MWCNTs) on the rheological behavior, early mechanical properties and volume stability of OWCP by means of different experimental methodologies. Multiple microstructural techniques are employed to further understand the reinforcing mechanism of MWCNTs on the performances of OWCP. The results show that the optimal dosage of MWCNTs is 0.6wt.‰. The rheological behavior of MWCNTs/OWCP slurry at low shearing rate is improved after the addition of 0.6wt.‰MWCNTs. The mechanical properties and autogenous shrinkage of MWCNTs/OWCP composites are enhanced after the addition of the optimal dosage of MWCNTs, MWCNTs/OWCP composites with addition of 0.6wt.‰MWCNTs exhibit more flexible and ductile than plain OWCP. The additional nucleation sites provided by MWCNTs, the role of bridging effect and pull-out effect by MWCNTs, and the high curing temperature are all responsible for the enhanced mechanical properties of MWCNTs/OWCP composites. Owing to the addition of MWCNTs, the relationship between the compressive strengths of MWCNTs/OWCP composites and gel/space ratios does not exhibit exponential form. However, the addition of MWCNTs does not alter the Avrami-type exponential relationship between the degree of hydration and curing ages, moreover, it does not alter the linear relationship between the mercury intrusion porosity and gel/space ratio.